Mold and imprint apparatus

ABSTRACT

In order to provide a mold and an imprint apparatus which permit adjustment of a depth of an imprint pattern after the imprint pattern is formed, the mold is constituted by a mold substrate including a first material and a surface layer, constituting a projection of the mold and including a second material, for forming a pattern on the photocurable resin material. The first material is more etchable than the second material. The first material and the second material have optical transmittances capable of curing the photocurable resin material with respect to at least a part of wavelength range of ultraviolet light.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to a mold and an imprint apparatus.

In recent years, a fine processing technology for transferring a finestructure on a mold onto a member to be processed, such as a resinmaterial or a metal material, has been developed and has receivedattention. This technology is called nanoimprint or nanoembossing andhas a dissolution on the order of several nanometers, so thatexpectations are growing that the technology is used as anext-generation semiconductor fabrication technology in place of a lightexposure apparatus such as a stepper or a scanner.

The technology can permit simultaneous processing of three-dimensionalstructure, so that it is expected to be applied to the followingproduction technologies other than the semiconductor fabricationtechnology. For example, the technology is expected to be applied tovarious fields of production technologies including those of opticaldevices such as photonic crystal and those of a biochip such as micrototal analysis system (μ-TAS).

Application of imprint processing to the semiconductor fabricationtechnology is described in, e.g., Stephan Y. Chou et al., Appl. Phys.Lett., Vol. 67, Issue 21, pp. 3114-3116 (1995). More specifically, awork or workpiece constituted by disposing a layer of a photocurableresin material on a substrate such as a semiconductor wafer is prepared.A mold having a processing surface (surface to be processed) on which adesired imprint pattern is formed is pressed against the work, followedby further pressure application and irradiation with ultraviolet light(ultraviolet rays) to cure the photocurable resin material. In thismanner, the pattern is imprinted onto the resin layer, so that the resinlayer is used as a mask to effect etching, thus performing patternformation on the substrate.

The processing by imprint is performed by transferring a shape ofimprint pattern including a recess and a projection formed on aprocessing surface of a mold onto a member to be processed. As asubstrate for the mold on which the imprint pattern is formed, quartz(silica or fused silica) is generally used. During etching of theimprint pattern at the processing surface of the mask including thequartz substrate, a layer (film) of Cr is generally used as a hard mask.As the material for the hard mask other than Cr, U.S. Patent ApplicationPublication No. US2003/0205658 has disclosed polysilicon and silicide.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a mold capable ofadjusting a depth of an imprint pattern of the mold after the mold isprepared.

Another object of the present invention is to provide an imprintapparatus including the mold.

According to an aspect of the present invention, there is provided amold for imprinting a pattern on a photocurable resin material,comprising:

a mold substrate comprising a first material; and

a surface layer, constituting a projection of the mold and comprising asecond material, for forming a pattern on the photocurable resinmaterial;

wherein the first material is more etchable than the second material,and wherein the first material and the second material have opticaltransmittances capable of curing the photocurable resin material withrespect to at least a part of wavelength range of ultraviolet light.

The mold according to the present invention is constituted so that it ispossible to effect imprint while leaving a hard mask, used for etching,as a surface layer without removing the hard mask during formation of animprint pattern onto a mold processing surface. Further, duringadjustment of a depth of the imprint pattern, the mold is constituted sothat the remaining surface layer can be used again as a mask foretching. Based on such a constitution, it is possible to adjust thedepth of the pattern of the mold after the mold is prepared.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view showing an embodiment of the moldaccording to the present invention.

FIGS. 2(a) to 2(e) are schematic sectional views for illustrating anembodiment of preparation steps of the mold of the present invention.

FIG. 3 is a schematic sectional view for illustrating the case where adepth of a recess of a mold is increased after the mold is prepared.

FIGS. 4(a) to 4(c) are schematic sectional views for illustrating thecase where a depth of a recess of a mold is decreased after the mold isprepared.

FIGS. 5(a) and 5(b) are schematic sectional views for illustratinganother embodiment of preparation steps of the mold of the presentinvention.

FIGS. 6(a) to 6(f) are schematic sectional views for illustrating apreparation process of a device using the mold of the present invention.

FIG. 7 is a schematic view for illustrating a constitution of an imprintapparatus including the mold of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A deep depth of a recess of a mold used in imprint processing is notalways better. For example, when a mold is pressed against a resin layeras a mask layer and then is removed from the resin layer, a shallowdepth of a recess of the mold permits easier removal of the mold. On theother hand, with respect to a performance of the resin layer, on which apattern is to be formed, as a mask layer, it is desirable that the moldrecess has a deeper depth since a thicker resin layer is usable. Inthese circumstances, in the case of effecting optimum imprint, it isnecessary to optimize a depth of an imprint pattern.

However, in order to change the depth of the imprint pattern of the moldafter the mold is prepared, there is no other way but to prepare a moldonce again. For this reason, further cost and time are required, thusbeing inefficient. This is because formation of the mold pattern withhigh definition by using an EB exposure apparatus which has beengenerally used requires much cost and time. Further, the cost and timerequired for the formation of the mold pattern are cumulativelyincreased for each additional preparation of mold.

In view of this problem, the inventors have come to recognition that itis possible to effect efficient imprint when the depth of the imprintpattern is adjustable after the mold is prepared.

In this regard, however, it is also possible to consider that a hardmask of Cr used during processing of mold is left without being removedand is used as a mold for adjusting a depth of the imprint pattern.However, the hard mask of Cr has a very low transmittance to ultravioletlight, so that it is difficult to cure a photocurable resin materialformed on a substrate by passing ultraviolet light through the hard maskof Cr.

Further, a hard mask of polysilicon or silicide used as the hard mask asdescribed in U.S. Patent Application Publication No. US2003/0205658 alsohas a very low transmittance to ultraviolet light. For this reason, itis similarly difficult to cure a photocurable resin material formed on asubstrate.

All the above described materials have very low transmittances toultraviolet light, so that the photocurable resin material is notreadily cured by irradiation of ultraviolet light through thesematerials. As a result, there arises such a problem that the uncuredresin material is adhered to the mold to result in contamination whichimpedes subsequent processing.

As described above, the conventionally used hard mask materials such asCr, polysilicon, and silicide are required to be removed before theimprint is effected. For this reason, they are not suitable for a maskfor additional etching which is performed after the mold is onceprocessed.

The mold according to the present invention includes a mold substrateformed of a first material and a surface layer constituting a projectionof the mold. The surface layer is formed of a second material and is alayer for forming a pattern on a photocurable resin material. The firstmaterial is more etchable than the second material. Further, the firstmaterial and the second material have optical transmittances capable ofcuring the photocurable resin material with respect to at least a partof wavelength range of ultraviolet light.

Hereinbelow, an embodiment of the present invention will be described.

As shown in FIG. 1, a mold 103 is constituted by a mold substrate 101formed of a first material and a surface layer 102 formed of a secondmaterial different from the first material.

The mold 103 has an imprint pattern formed at the surface of the moldsubstrate 101 and has a projection at which the surface layer 102 isprovided. The surface layer 102 is formed by leaving a hard mask, usedwhen the imprint pattern is formed at a processing surface of the mold103, as it is without removing the hard mask.

In other words, the surface layer 102 is a layer which remains on themold substrate 101 without being removed when the imprint is performedand which is used for pattern formation of a photocurable resinmaterial. Further, the surface layer 102 is also a layer functioning asa mask during adjustment of a depth of the pattern of the mold after theimprint is effected.

When the surface layer 102 is used for the pattern formation of thephotocurable resin material, it may directly contact the photocurableresin material. Further, the surface layer 102 may also indirectlycontact the photocurable resin material through a release agent appliedonto the surface layer 102. The surface layer 102 may be constituted ina single layer form or a multilayer form.

The first material for the mold substrate 101 and the second materialfor the surface layer 102 have optical transmittances capable of curingthe photocurable resin material with respect to light in at least a partof wavelength range of ultraviolet light. As a result, the photocurableresin material can be cured, so that it is possible to effect imprint ofthe pattern formed on the mold surface. As the first material for themold substrate 101, it is possible to use silicon oxide etc. As thesecond material for the surface layer 102, it is possible to use siliconnitride, titanium oxide, aluminum oxide, calcium fluoride, indium tinoxide (ITO), zinc oxide, etc.

Incidentally, the photocurable resin material is basically cured byincreasing an amount of light exposure unless an optical transmittanceto ultraviolet light is zero. However, in view of an actual throughput,a somewhat high transmittance is required. For example, in the casewhere a light source emitting light at a wavelength of 365 nm is used asa light source used for a photocuring process, a film of silicon oxideused as the first material for the mold substrate 101 described abovehas an optical transmittance of approximately 90% with respect to the365 nm wavelength light. Accordingly, in order not to considerably lowera throughput compared with the case of silicon oxide as the firstmaterial for the mold substrate 101, it is desirable that the surfacelayer 102 at least has an optical transmittance of not less than 30%.

Further, when the mold substrate 101 and the surface layer 102 provide alarge difference in optical transmittance, there is a possibility thatan irregularity in degree of curing of the photocurable resin materialis caused to occur. For this reason, the transmittances of bothmaterials may preferably be as close as possible. In a more preferredembodiment, the second material for the surface layer 102 has an opticaltransmittance of not less than 80%.

Further, in order to effect the adjustment of depth of the imprintpattern of the mold after the mold is prepared, it is necessary for thefirst material and the second material to be a combination such that thefirst material is more etchable than the second material.

In order to selectively remove the first material, it is necessary toincrease an etching rate of the first material for the mold substrate101 compared with an etching rate of the second material for the surfacelayer 102. In the present invention, the first material may besubstantially removed selectively, so that some degree of the secondmaterial may also be removed. The etching rate can be represented by aratio of etched layer thickness to etching time (e.g., nm/min).

In this embodiment, in order to selectively remove the first material,by etching, compared with the second material, it is possible to employreactive ion etching using gas having a high C/F ratio, such as those ofC₃F₈, C₄F₈, C₅F₈, and C₄F₆, as source gas. In the case there the firstmaterial for the mold substrate 101 is silicon oxide and the secondmaterial for the surface layer 102 is silicon nitride in the abovedescribed treatment condition, a ratio of etching rate of first materialto etching rate of second material is approximately 10-30. Further, inthe same treatment condition, the etching rate ratio of silicon oxide toa resist is approximately 3-8. Incidentally, in the case where thesurface layer 102 is thinner than the resist mask layer, the etchingrate ratio may desirably be not less than 20.

Further, in the case of employing wet etching, it is possible to use,e.g., hydrofluoric acid. The wet etching is effective in formation of apattern having a width exceeding several ten micrometers.

The depth of the mold varies depending on a width of a pattern to beformed but may preferably provide an aspect ratio, defined as (depth ofmold)/(minimum width of pattern to be formed), of 0.5-10. Further, aratio of the thickness of surface layer 102 to the depth of mold 103 maypreferably be not less than 20%, e.g., in the case where the etchingrate ratio is not less than 10 and the number of depth adjustment is notless than 3. The thickness of the mold substrate 101 may desirably benot less than several micrometers in consideration of mechanicalstrength.

As described above, the present invention is characterized in that thesurface layer is not removed when the mold is completed, so that it ispossible to adjust a depth of a recess of the mold even after theimprint is effected. In the mold preparation process, a step requiringmuch cost and time is a step of forming the imprint pattern. Accordingto the present invention, it is possible to variably change the depth ofthe recess of the mold after the imprint is effected, so that it is notnecessary for the mold to be prepared again from scratch. Accordingly,it is possible to reduce cost and time required for the patternformation step.

Hereinafter, the present invention will be described based onembodiments.

Embodiment 1

A production process of a mold according to the present invention willbe described in Embodiment 1. FIGS. 2(a) to 2(e) are sectional views forillustrating preparation steps of a mold 103 in this embodiment.

(1) A surface layer 102 is formed in a film on a mold substrate 101(FIG. 2(a)). As a first material for the mold substrate 101, siliconoxide or the like is used. As a second material for the surface layer102, it is possible to use silicon nitride, titanium oxide, aluminumoxide, calcium fluoride, indium tin oxide (ITO), zinc oxide, etc. Thesurface layer 102 may also be formed in a multilayer form in addition tothe single layer form.

(2) On the surface layer 102, a resist 201 is disposed and patterned(FIG. 2(b)). The patterning may be effected by utilizing light exposurewith a stepper or a scanner or electron beam drawing.

(3) The surface layer 102 is etched (FIG. 2(c)).

(4) After the resist 201 is stripped, the mold substrate 101 is etchedwith the surface layer 102 as a mask layer (FIG. 2(d)). The etching isperformed by reactive ion etching using gas having a high C/F ratio suchas C₃F₈, C₄F₈, C₅F₈ or C₄F₆, as source gas as described above.Incidentally, the mold substrate 101 may also be etched by leaving theresist 201 and using the surface layer 102 and the resist 201 as themask layer.

In another embodiment, it is also possible to prepare a mold of thepresent invention by stripping the resist 201 and then not subjectingthe mold substrate 101 to etching (FIG. 2(e)). In this case, the surfacelayer 102 constitutes the entire projection of the mold 103.

In the above embodiment, the surface layer 102 is formed on the moldsubstrate 101 and thereon the resist 201 is formed. The surface layer102 may also be provided by using a so-called lift-off method. Morespecifically, the resist 201 is formed on the mold substrate 101 and ispartially removed by etching. Then, after the surface layer 102 isformed, the resist is stripped and then the mold substrate 101 isetched. In this manner, it is also possible to prepare the moldaccording to the present invention.

As described above, the mold 103 having the surface layer 102, which hasbeen used as the hard mask during formation of an imprint pattern on aprocessing surface, left on the mold substrate 101 as shown in FIG. 1 isprepared.

The first material of the mold substrate 101 and the second material forthe surface layer 102 which constitute the mold 103 have opticaltransmittances capable of curing a photocurable resin material withrespect to light in at least a part of wavelength range of ultravioletlight.

Accordingly, even when the surface layer 102 is not removed but left onthe mold substrate 101, it is possible to transfer the imprint patternof the mold 103 onto the photocurable resin material.

Incidentally, in the conventional case where the Cr layer is used as thehard mask for forming the imprint pattern on the mold processing surfacethrough etching and is subjected to etching for re-processing whilebeing left on the mold substrate without being removed, there is concernabout an occurrence of metal contamination. However, in this embodiment,there is no such concern.

Embodiment 2

A method of adjusting a depth of an imprint pattern of the moldaccording to the present invention after the mold is prepared will bedescribed in Embodiment 2.

FIG. 3 is a sectional view for illustrating an embodiment in the case ofincreasing a depth of a recess of the mold after the mold is prepared.

In this case, additional etching of the mold substrate 101 is onlyeffected by using the etching method described in Embodiment 1 whileusing the surface layer 102 as a mask layer. More specifically, aportion 301 at the recess of the mold substrate 101 is etched togetherwith a portion 302 of the surface layer 102.

FIGS. 4(a) to 4(c) are sectional views for illustrating an embodiment inthe case of decreasing the depth of the recess of the mold after themold is prepared.

(1) On the entire surface of the mold 103, a material 401 identical tothat of the mold substrate 101 is formed in a layer so as to fully fillthe recess of the mold 103 (FIG. 4(a)).

(2) The resultant structure is etched and flattened by etching a portion402 of the layer 401 (FIG. 4(b)), thus exposing the surface of the mold103 (FIG. 4(c)).

(3) By employing the etching method described in Embodiment 1, theremaining portion of the layer 401 is etched. More specifically, aportion 403 of the layer 401 is etched together with a portion 404 ofthe surface layer 102 (FIG. 4(c)).

As described above, it is possible to appropriately adjust the depth ofthe recess of the mold 103 after the mold 103 is prepared.

Embodiment 3

A modified embodiment of a production process of the mold according tothe present invention will be described in Embodiment 3.

FIGS. 5(a) and 5(b) are sectional views for illustrating the modifiedembodiment of the mold production process.

In the case of effecting re-processing of the mold as in the casedescribed with reference to FIGS. 3 and 4(a) to 4(c), the portions 302and 404 of the surface layer 102 can also be somewhat etched. For thisreason, the thickness of the surface layer 102 may desirably beincreased. However, when a thick surface layer 102 is etched with theresist 201 as the mask layer, a shape of a side wall portion is deformedto lower an accuracy of pattern to be transferred onto the moldsubstrate 101 is some cases. For this reason, as shown in FIG. 5(a), anadditional hard mask layer 501 is provided between the resist 201 andthe surface layer 102.

Next, by using the resist 201, the hard mask layer 501 is etched andthen the surface layer 102 is etched using the hard mask layer 501 as amask layer (FIG. 5(b)).

As a material for the hard mask layer 501, it is suitably possible touse a metal material such as Cr, WSi or Al. There is no problem evenwhen the hard mask layer 501 is left on the surface layer 102 duringetching of the mold substrate 101 in a subsequent step. However, thehard mask layer 501 is removed at least before imprint.

Embodiment 4

In Embodiment 4, a device production process using the mold of thepresent invention and an imprint apparatus including the mold of thepresent invention will be described.

FIGS. 6(a) to 6(f) are sectional views for illustrating production stepsfor effecting imprint of an imprint pattern.

First, onto a substrate 601, a photocurable resin material 602 isapplied (FIG. 6(a)). Next, the mold 103 and the substrate 601 are causedto come close to and contact each other (FIG. 6(b)). The resultantstructure is irradiated with ultraviolet light 603 from a back side ofthe mold 103 to cure the photocurable resin material 602 (FIG. 6(c)).Thereafter, the mold 103 is moved away from the substrate 601 (FIG.6(d)), and a pattern is transferred onto the substrate 601 by etching(FIG. 6(e)). Finally, when the photocurable resin material 602 isremoved from the substrate 601, the pattern is formed on the substrate601 (FIG. 6(f)).

In the case of preparing a semiconductor device, examples of thematerial for the substrate 601 or its surface layer may include silicon,silicon oxide, silicon nitride, silicon carbide, an insulating film oflow dielectric constant (low-k) material, aluminum, copper, galliumarsenide, gallium nitride, etc. Further, in the case of preparingphotonic crystal, as the material for the substrate 601, it is possibleto use silicon, titanium oxide, gallium nitride, etc. Further, in thecase of preparing a biochip, as the material for the substrate 601, itis possible to use silicon, silicon oxide, etc.

FIG. 7 shows a constitution of the imprint apparatus including the moldof the present invention.

Referring to FIG. 7, the imprint apparatus includes an exposure lightsource 701, a mold holding portion 702, a work holding portion 703, awork pressing mechanism 704, an in-plane moving mechanism 705, and animprint control mechanism.

By the work pressing mechanism 704, the mold 103 and the substrate 601are caused to contact each other through the photocurable resin material602.

Ultraviolet light emitted from the exposure light source 701 passesthrough the mold holding portion 702 and the mold 103 in this order andcures the photocurable resin material 602. Then, the mold 103 and thesubstrate 601 are moved away from each other by the work pressingmechanism 704. As desired, after the substrate 601 is moved by thein-plane moving mechanism 705, a so-called step-and-repeat method inwhich transfer of the pattern in an area adjacent to thepattern-transferred area is performed again is effected.

Incidentally, the work pressing mechanism 704 and the in-plane movingmechanism 705 may also be provided on the mold holding portion 702 side.

Embodiment 5

In Embodiment 5, a mold in which the first material and the secondmaterial described above have optical transmittances capable of beingoptically measured will be described.

As described above, efficient imprint can be effected when the depth ofthe imprint pattern is adjustable after the mold is prepared. In thisregard, in the conventional embodiment, as the mold for the hard maskused during the processing of mold, it was possible to use Cr,polysilicon, silicide, etc. It is also possible to consider that thehard mask is used as a mask for adjusting the depth of the imprintpattern without being removed.

However, these materials (Cr, polysilicon, and silicide) have very lowtransmittances to visible light. For this reason, e.g., in the casewhere a visible light source is used as a light source for observing analignment mark, such a problem that alignment using the mold is notreadily effected arises.

In this embodiment, the mold is a mold for imprinting a pattern on aresin material such that it includes a mold substrate formed of a firstmaterial; and a surface layer, constituting a projection of the mold andformed of a second material, for forming a pattern on the photocurableresin material. The mold is characterized in that the first material ismore etchable than the second material, and wherein the first materialand the second material have optical transmittances capable of beingoptically measured.

As the material for the mold substrate, similarly as in Embodiment 1,silicon oxide or the like can be used. Further, as the material for thesurface layer, similarly as in Embodiment 1, it is possible to usesilicon nitride, titanium oxide, aluminum oxide, calcium fluoride, ITO,zinc oxide, etc.

The mold in this embodiment is also applicable to other opticalmeasurements, such as those for a reflectance at the substrate surface,an interference of distance between the mold and the substrate, andabsorptivity of resin material.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purpose of the improvements or the scope of thefollowing claims.

This application claims priority from Japanese Patent Applications Nos.257394/2005 filed Sep. 6, 2005 and 194266/2006 filed Jul. 14, 2006,which are hereby incorporated by reference.

1. A mold for imprinting a pattern on a photocurable resin material,comprising: a mold substrate comprising a first material; and a surfacelayer, constituting a projection of said mold and comprising a secondmaterial, for forming a pattern on the photocurable resin material;wherein the first material is more etchable than the second material,and wherein the first material and the second material have opticaltransmittances capable of curing the photocurable resin material withrespect to at least a part of wavelength range of ultraviolet light. 2.A mold according to claim 1, wherein the first material and the secondmaterial have a ratio of an etching rate of first material to an etchingrate of second material of not less than
 10. 3. A mold according toclaim 1, wherein the second material has an optical transmittance, tolight at a wavelength of 365 nm, of not less than 30%.
 4. A moldaccording to claim 1, wherein said surface layer constitutes a part ofthe projection of said mold.
 5. A mold according to claim 1, whereinsaid surface layer constitutes all of the projection of said mold.
 6. Amold according to claim 1, wherein the first material is silicon oxideand the second material is selected from the group consisting of siliconnitride, titanium oxide, aluminum oxide, calcium fluoride, and indiumtin oxide.
 7. An imprint apparatus for effecting imprint by irradiatinga photocurable resin material with ultraviolet light through a mold tocure the photocurable resin material, comprising: as the mold, a moldaccording to claim
 1. 8. A process for producing a device, comprising:preparing a mold according to claim 1; causing the mold to contact aphotocurable resin material; and irradiating the photocurable resinmaterial with ultraviolet light through the mold.
 9. A mold forimprinting a pattern on a resin material, comprising: a mold substratecomprising a first material; and a surface layer, constituting aprojection of said mold and comprising a second material, for forming apattern on the photocurable resin material; wherein the first materialis more etchable than the second material, and wherein the firstmaterial and the second material have optical transmittances capable ofbeing optically measured.
 10. A mold for imprinting a pattern on aphotocurable resin material, comprising: a mold substrate comprising afirst material; and a surface layer, constituting a projection of saidmold and comprising a second material, for forming a pattern on thephotocurable resin material; wherein the first material is more etchablethan the second material, and wherein the first material and the secondmaterial have optical transmittances capable of curing the photocurableresin material.